The present invention generally relates to copolymers that serve as structural supplements in injectible bodily prosthetics employed in medical or cosmetic procedures. The present invention further relates to injectible polymeric nucleus pulposus replacement materials, and the use of such materials in treating degenerative intervertebral disc disorders and spinal injuries.
The intervertebral disc is a complex joint anatomically and functionally. It is composed of three component structures: the nucleus pulposus, the annulus fibrosus and two vertebral end-plates. The nucleus pulposus is a generally loose or amorphous hydrogel which serves to support the load applied to the disc, and is mainly responsible for the compressive properties of the disc. The annulus fibrosus forms the outer limiting boundary of the disc, and serves to maintain the nucleus pulposus in compression while inhibiting over-rotation of the disc. The vertebral end-plates are composed of hyaline cartilage, and separates the disc from the adjacent vertebral bodies. This layer acts as a transitional zone between the hard, bony vertebral bodies and the soft disc.
Damage or displacement to the intervertebral disc may be caused by trauma, disease, or an inherent disorder. In these cases, the nucleus pulposus may herniate and/or protrude into the vertebral canal or intervertebral foramen, resulting in back pain and/or loss of mechanical spinal function.
Current treatment options include conservative bed rest, a laminectomy (removal of the disc), as well as highly invasive surgical procedures, such as spinal fusion. Although these treatments offer pain relief, they do not restore the mechanical function of the spine. Other options involve replacing the damaged or degenerated disc with a synthetic disc implant, such as Charite. Unfortunately, such disc replacements often lead to stress shielding and other deleterious effects, as well as highly invasive surgery.
Nucleus pulposus replacement is one possible treatment for disc injuries and other degenerative disc disorders. Nucleus pulposus replacement typically involves the replacement of the damaged pulposus with a prosthetic nucleus pulposus. For example, U.S. Pat. No. 5,047,055 to Bao et al., which is incorporated herein by reference, describes the use of a hydrogel prosthetic nucleus as a treatment for disc injuries and other degenerative disc disorders. The hydrogel is prepared by cast molding or lathecutting, and then implanted in conjunction with a laminectomy operation, such as discectomy or microdiscectomy, percutaneous discectomy, or chemonucleolysis. All of which require an invasive surgery.
What is needed is a new hydrogel replacement system that is less invasive.